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(require '[clojure.set])
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(defn get-adj
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"Gets vector of coords surrounding (x, y)."
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[y x] [[(dec y) x] [(inc y) x] [y (dec x)] [y (inc x)]])
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(defn basin-continues?
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"Determines if `b` is a continuation of the basin that includes `a`."
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[a b] (and (some? b) (not= b 9) (> b a)))
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(defn basin-bottom?
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"Determines if point `p` in `hmap` is the bottom of a basin surrounded by
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points `adj`."
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[hmap p adj]
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(every?
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#(let [q (get-in hmap %)] (or (nil? q) (< (get-in hmap p) q)))
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adj
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))
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(defn find-basin
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"If point `yx` in `hmap` is in a basin (determined using `adj`), return a
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list of points in the basin that are above `yx`."
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[hmap yx adj]
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(let [res (filter #(basin-continues? (get-in hmap yx)
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(get-in hmap %))
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adj)]
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(apply (partial clojure.set/union res)
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(map #(set (find-basin hmap % (apply get-adj %))) res)
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)))
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(->> (slurp "./in")
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(clojure.string/split-lines)
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(mapv vec)
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(mapv (partial mapv #(- (int %) 48)))
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(#(for [y (range 0 (count %))
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x (range 0 (count (first %)))
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:let [adj (get-adj y x)]
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:when (basin-bottom? % [y x] adj)]
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(inc (count (find-basin % [y x] adj)))))
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(sort >)
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(take 3)
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(apply *)
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(println)
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)
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